According to the usual method of manufacturing drawn and ironed cans, cups are first drawn from circular blanks of flat stock. The cups have the wall thickness of the original stock. The cups are placed on a punch of a diameter corresponding to the inside diameter of the finished can, and passed through stationary ring like ironing dies to reduce and elongate the side walls of the cup to the dimensions required for the finished can.
The stationary ring dies presently used develop sliding friction with the can wall and a considerable amount of heat is generated. Furthermore the stress of forcing the can through the die is carried by the reduced portion of the can wall. Because of these factors, the speed at which the ironing process can be carried out, and the amount of reduction which can be accomplished in one pass are limited. Customarily two or more ironing rings of successively smaller inner diameter are used to reduce the can wall to the finished thickness.
The use of stationary rings in the ironing process also causes other problems. Pinholes in the material may be enlarged to the point of producing a defective can. Wear on the dies is considerable, so that they have to be periodically removed and refinished. In doing so the inner diameter is enlarged so that matched sets of punches and dies must be used to maintain uniform wall thickness in the cans. In the case of steel, for example of the type known as black plate, the presence of precipitated carbides can cause damage to the dies.
The principal object of this invention is to achieve a considerable reduction in the friction generated between an ironing die and the can wall during the ironing process, thus reducing the problems associated with high friction, and prolonging the life of the dies. Another object is to provide a die which tends to close rather than enlarge pinholes and to distribute precipitated carbides and minimize their effect. Another object is to provide a die which can be refinished to its original diameter. Other objects, advantages, and novel features will be apparent from the following description.